Display device for projector and method of making and using a display device

ABSTRACT

A liquid crystal display includes plural liquid crystal picture elements selectively operable to affect light by scattering or absorbing light or by reducing such scattering or absorption of light, a separator integral with and between respective picture elements, the separator being substantially non-selectively operable to affect light and including spacers between respective picture elements forming a grid of spacers and picture elements and overlying parts of respective driving TFT transistors or the like so they do not detrimentally affect an image or in effect mask out drive elements from being seen in the displayed image or projected image. The liquid crystal may have a birefringence in the range of about 0.12 or less and may be used in a projection system in which an image is formed from nonspecular light.

CROSS REFERENCE TO THE RELATED PATENT APPLICATIONS

This application is a national stage of PCT/US98/26766, filed Dec. 17,1998, which claims priority from application Ser. No. 60/068,265, filedDec. 19, 1997; the priority of both are claimed.

Reference is made to applicant's commonly owned U.S. patent applicationSer. No. 60/040,764, filed Mar. 14, 1997, the entire disclosure of whichhereby is incorporated by reference, and the priority of which isclaimed.

TECHNICAL FIELD

This invention relates, generally, as is indicated, to a display deviceor element for projectors or other optical devices or systems, and, moreparticularly, to a display device or element having a mask or separatorbetween respective picture elements and to methods of making and usingthe display device or element. This invention also relates to projectorsusing such display devices.

BACKGROUND

Projectors are used for business, education, diagnostics, entertainmentand other purposes to project images from an image source onto a screenor the like for viewing. Many different types of projectors are known,some examples being slide projectors, movie projectors, overheadprojectors, and so forth. In some projectors an image which is fixed ona film, slide, or the like, is projected onto a viewing screen. Inanother type of projector an image is developed or formed in a medium,such as a liquid crystal device, and the image is projected onto aviewing screen; sometimes these are referred to as liquid crystalprojectors.

One example of liquid crystal projector uses a twisted nematic liquidcrystal cell to modulate light from a light source to produce an imagefor projection. In such a projector polarized light is selectivelytransmitted or blocked by the cooperative relation between a twistednematic liquid crystal cell and an optical polarizer.

Another example of liquid crystal projector uses the principle ofselective scattering or transmitting of light by a liquid crystal devicein cooperation with an optical aperture and stop to discriminate betweentransmitted and scattered light to provide an image for projection. Aliquid crystal device sometimes referred to as NCAP, PDLC, LCPC andpossibly by other names is useful to provide the selective lightscattering or transmitting in such a projector. One example of such aprojector is disclosed in U.S. Pat. No. 4,613,207. Several examples ofliquid crystal materials or devices useful in such a projector aredisclosed in U.S. Pat. Nos. 4,435,047, 4,606,611, 4,688,900, and4,728,547. For brevity, such materials and devices which are operable toscatter light or to transmit light collectively may be referred to belowas NCAP materials or NCAP devices, and liquid crystal projectors usingNCAP materials collectively may be referred to below as an NCAP basedLCD projector (“LCD” being a conventional shorthand for liquid crystaldisplay or liquid crystal device) or more simply as NCAP projector.

NCAP projectors which use the switchable light scattering properties ofNCAP materials to modulate light have been demonstrated for example, asis disclosed in U.S. Pat. No. 4,613,207. In one embodiment of aprojector disclosed in the '207 patent the light source is focused ontoa small aperture located in a plate or mask between the projection lensand an NCAP device which is operable as a display to form an image. Ifthe NCAP device (or a picture element, pixel or other part thereof) isin a clear (non-scattering light transmitting) state, substantially allof the light from the NCAP device (or from the indicated pixel) passesthrough the aperture and is collected and projected by the projectionlens. Such transmitted light sometimes is referred to as specular lightor specularly transmitted light. Light scattered by the NCAP device orfrom one or more pixels thereof (sometimes referred to as scatteredlight) is redirected away from the aperture and is blocked or stopped bythe plate in which the aperture is located. In such a projector some ofthe scattered light may also impinge on and pass through the aperture;this light leakage can reduce contrast of the output. It would bedesirable to improve contrast, for example, to increase the contrast orcontrast ratio between bright and dark areas of a projected image.

Another embodiment of NCAP projector disclosed in the above '207 patentuses Schlieren optics. A projector which uses Schlieren optics may bereferred to as a Schlieren projector, Schlieren optics projector or darkfield projector. The Schlieren optics discriminate between light that istransmitted and light that is scattered by a display; the Schlierenprojector projects scattered light and blocks transmitted light. Anadvantage of a Schlieren projector is an improved dark field, which canlead to higher contrast. One reason for such contrast improvement isimproved discrimination between the light which is scattered by the NCAPdevice and the light which is transmitted by that device (specularlight); the scattered light is collected and used in the output image,but the transmitted light (specular light) is blocked by a mask or stopin the light path and, therefore, does not reduce contrast.

Various display devices have been used as a “light engine” to create animage for projection, for example using various of the above-mentionedprojectors. For example, in U.S. Pat. No. 5,519,524 is disclosed aminiature image source in which electrical input is provided by anelectrical drive which includes respective electrodes and transistorsassociated therewith in an active matrix type liquid crystal display.The electrodes and transistors of the active matrix display are formedin/on a semiconductor substrate, sometimes referred to as an activematrix or a TFT (thin film transistor) device or as an active matrixsubstrate; one or more counter electrodes are opposite the respectiveactive matrix electrodes. Respective picture elements are formed by thecounter electrode and respective electrodes and the liquid crystalmaterial therebetween. Alignment of liquid crystal material betweenrespective active matrix electrodes and counter electrode(s) can beaffected by providing electric field between the electrodes; andcharacteristics of polarized light, e.g., the direction of polarization,transmitted through the miniature image source can be changed or notdepending on whether or not a field is applied and the magnitude of thefield. Another example of an active matrix (or TFT) type of displaydevice is disclosed in U.S. Pat. No. 5,532,854.

Advantages of size, power, manufacturing, resolution, and so forth,inure to active matrix (TFT) type display systems. Such systems arereferred to as electronic input type display systems. Another type ofelectronic input type display system is referred to as MIM. Others alsomay exist, may be developed in the future and may be useful in theinvention.

In electronic input type display systems it is necessary to providespace between respective active matrix transistors and electrodesdirectly associated therewith, thus, providing space between respectiverelatively adjacent picture elements. Such space provides electricalinsulation or isolation and is an area in which conductors or conductivepaths may be located to connect to respective transistors or other partsof the device. Such space usually is not active to present changeableimage characteristics of the optical output of an active matrix displaydevice and may be referred to as optically dead space.

In a reflective electronic type display system there usually is sometype of reflector or reflective surface or material to reflect light.For example, electrodes may be reflective or include a reflectivecoating or treatment and/or a separate reflector may be provided, as isknown. Sometimes light which is incident on the optical dead space alsois reflected. Thus, light incident on such reflector is reflected backin the opposite direction; if the incident light impinges on thereflective surface at an angle other than normal, the angle of incidencewill be the same or substantially the same as the angle of reflection asis the case for conventional reflectors and if the incident light isincident normal to the reflector. Where the light is transmitted throughliquid crystal material the light may or may not have changedpolarization characteristics, depending on the current alignment of theliquid crystal material; but where the light is incident on opticallydead space and reflects back from that space, the polarizationcharacteristics of the light usually would not be altered as a functionof electrical input, as there is no electrode there to apply electricfield. Therefore, the existence of the optically dead space may have adetrimental affect on the resolution and/or contrast of the opticaloutput.

A scattering type liquid crystal system may include a liquid crystaldisplay, such as NCAP material or an NCAP display, and a drive device,such as an electronic drive, for example, an active matrix, thin filmtransistor (TFT), metal insulator metal (MIM) or some other drive devicefor the display. In a reflective type of NCAP display system, opticallyreflective portions reflect light passed through the display device backthrough the display device for output as scattered or as unscattered(transmitted) light. It has been discovered that due to scatteringcaused by portions of the liquid crystal display device which arealigned with the optically dead spaces or with certain components orelements in the optically dead spaces of the drive unwanted scatteredlight may be projected by a Schlieren optics projector. Such scatteredlight may bypass the stop so as to be projected, which reduces thecontrast or contrast ratio of the projected image. Accordingly, it wouldbe desirable to eliminate from projection scattered light which does notderive from intended picture elements or areas of the display.

SUMMARY

Briefly, according to an aspect of this invention, a separator or maskis provided between picture elements and/or in the area of opticallydead space of the display or image forming device used in a Schlierenoptics projector system.

According to another aspect, the projecting of light from optically deadspace in a Schlieren optics projector is reduced or eliminated byreducing or preventing light scattering in the area of the opticallydead space.

According to another aspect of the invention, a liquid crystal displaydevice that is selectively operable to scatter incident light or toreduce the amount of scattering has plural picture elements, pixels orareas (hereinafter referred to as “picture elements” for convenience) towhich electrical input, such as an electric field or other electricalinput, magnetic input, etc., can be applied to cause a desired physicaland/or optical effect. A mask, divider or separator (hereinafter usuallyreferred to as “separator” for convenience) is between respectivepicture elements. The separator does not ordinarily change its opticalcharacteristics when the optical characteristics of the liquid crystaldevice changes its characteristics, and therefore it is possible tofilter out or to discriminate out light therefrom, as is described ingreater detail below. Light that is delivered as an output by the liquidcrystal device may include light that is scattered and/or light that isnot scattered. A Schlieren optics system associated with a projectordiscriminates between the scattered light and non-scattered light(sometimes referred to as “unscattered” transmitted or “specular” light)and delivers the appropriate light for projection. In an embodiment thescattered light, e.g., the light which is scattered at least outside,beyond or at greater than a predetermined angle or that is in any eventpassed by the Schlieren optics system, is projected. The separator isselected as not to scatter light. Therefore, light from the separatorwhich is delivered to the Schlieren optics system is blocked fromprojection. The projected light, then, is substantially exclusively thescattered light and contrast ratio of the projected image is enhanced.

According to another aspect of the present invention, a separator,divider or mask (hereinafter referred to by any of these terms) isbetween respective picture elements or areas of a liquid crystaldisplay. The separator is aligned with the dead space of the electricaldrive of the display system used in a Schlieren optics projector. Theseparator preferably does not ordinarily change optical characteristicsas the inputs to the picture elements of the liquid crystal display arechanged. In an embodiment the separator is does not scatter light or isat least substantially non-scattering whereas portions of the displaycan be scattering or non-scattering to create an image for projection.Light which is not scattered can be discriminated by Schlieren opticsand blocked from projection, whereas scattered light can be projected tocreate a projected image on a screen.

According to another aspect a liquid crystal material is at least partlydissolved in a medium. The combination of liquid crystal material andmedium is applied to an electrical drive, such as an active matrixsubstrate. The liquid crystal and medium is cured, dried, cross-linked,etc., in a controlled manner to form therein both areas of pictureelements 53 which are operable selectively to scatter light or to reducescattering and separators, which do not change optical characteristics,between respective picture elements.

In an embodiment of the invention, the separator is of the same materialas the medium of the liquid crystal display device, e.g., the medium inwhich the liquid crystal material is contained or with which the liquidcrystal material is cooperative to provide optical output. However,preferably the medium forming the separator does not include liquidcrystal material; or, alternatively, the separator does not includeliquid crystal material that in use of the liquid crystal display systemwould change alignment and/or affect on light.

In an embodiment an exemplary electrical drive device for the liquidcrystal device is a solid state device, such as an active matrix device,thin film transistor (TFT) device, metal insulator metal (MIM) device,or other device which has sections for applying input to a nearbypicture element of the liquid crystal display device, e.g., a pictureelement aligned with respect to a respective section. Such sections maybe, for example, electrodes and associated transistors and/or otherdevices for applying the prescribed input to the liquid crystal device.Between such sections there usually is optically dead space forelectrical leads, for electrical insulating purposes, for othercomponents of the drive, etc. The separator may be aligned with suchspace, and, since the Schlieren optics is able to block the projectingof light from the area of such divider or separator, the effect of thespace and/or of the separator, such as reflected light from a reflectoror components in the space and transmitted by the separator, is notprojected and does not have an impact on the projected image.

In the above copending U.S. patent application are describedimprovements to a liquid crystal projector which uses an opticsarrangement, sometimes referred to as Schlieren optics, in whichscattered light is projected and transmitted light (specular light) isblocked.

Briefly, as is described in such copending patent application, an NCAPprojector may use optics in which scattered light is projected andspecular light is blocked; and a liquid crystal device for selectivelytransmitting or scattering light through a relatively controlled angle.The control of the scattering angle may be by using relatively lowbirefringence liquid crystal material in an NCAP device and/or byrelatively accurately controlling the size of volumes of liquid crystalin the liquid crystal device. A number of advantages may inure to such aprojector, such as, for example, an improved dark field, which leads tohigher contrast, good light collection efficiency, tolerance of highintensity light sources, which leads to high brightness, and the abilityto use very thin NCAP devices, which may reduce voltage driverequirements relative to a thicker device.

One or more of the following aspects or features may be included in theinvention of the mentioned copending application and in the invention ofthe present application:

(A) The simple center hole aperture of prior projectors which projectlight transmitted by the liquid crystal device is replaced by a ringaperture with a stop in the center. The stop in the center of the ringaperture may be the same size as the original simple hole aperture (ormay be some other size). The specular light is blocked by the stop andthe scattered light passes through the ring to be captured by theprojection lens. The contrast in this type of projector may be increasedrelative to projectors with center hole apertures by minimizing thebrightness of the dark state.

(B) Brightness of the dark state may be reduced or minimized by reducingor minimizing the residual haze of the full on state (transmissive mode)of the NCAP device. This can usually be done by collimating the lightincident on the liquid crystal device so that the light would havenormal incidence and, therefore, be well collimated as it passes throughthe NCAP device.

(C) A projection system includes a source of collimated (parallel)light, a liquid crystal device for selectively transmitting light orscattering light through a relatively controlled angle, and an aperturearrangement for transmitting scattered light while blocking specularlytransmitted light.

(D) A projector includes a source of collimated light, a liquid crystalmeans for selectively transmitting light or scattering light through arelatively controlled angle, the liquid crystal means includesrelatively low birefringence liquid crystal in a containment medium, andthe liquid crystal having an ordinary index of refraction substantiallymatched to the index of refraction of the containment medium, focusingmeans for focusing the collimated light substantially to a point, a stopfor blocking light directed to that point, and an opening fortransmitting scattered light to form an image beyond that point.

(E) A method of controlling the angle of scattering of output light in aliquid crystal device includes controlling, limiting or selecting thebirefringence of the liquid crystal material which cooperates withanother medium and selectively scatters light or transmits light, thecontrolling, limiting or selecting comprising placing in physicalrelation with the medium, liquid crystal material that has abirefringence of about 0.12 or less.

(F) A projection system in which an image is formed from nonspecularlight includes a collimated light input, a liquid crystal deviceincluding liquid crystal material for selectively specularlytransmitting light or non-specularly scattering light, projection opticsfor receiving non-specularly scattered light for projection, means toblock the specularly transmitted light from projection by the projectionoptics, and wherein the angle of non-specular scattering is controlledby limiting the liquid crystal material to a birefringence that is about0.12 or less.

(G) A projection system in which an image is formed from nonspecularlight includes a collimated light input, a liquid crystal deviceincluding low birefringence liquid crystal material in volumes in acontainment medium for selectively specularly transmitting light ornon-specularly scattering light, projection optics for receivingnon-specularly scattered light for projection, means to block thespecularly transmitted light from projection by the projection optics,and wherein the angle of non-specular scattering is controlled bylimiting the size of the volumes to about 5 microns or less.

(H) A projection method includes selectively scattering light over arelatively controlled angle or specularly transmitting light, blockingthe specularly transmitted light, and directing the scattered light toprovide an output image.

(I) A method of getting collimated light into a liquid crystal devicethat is operable selectively to scatter light or to transmit lightwithout substantial scattering includes directing light from a lightsource to a beam splitter, reflecting light from the beam splitter to acollimating lens, directing the collimated light into the incident sideof a liquid crystal device.

(J) A method of projecting a relatively high contrast image includesdirecting collimated light through a liquid crystal device that providesselectively transmitting of light or controlled scattering of light,using Schlieren optical system discriminating between transmitted lightand scattered light, and projecting the scattered light to form anoptical output.

In accordance with an aspect of the present invention a scattering typeliquid crystal display device includes liquid crystal material that isselectively operable by a drive (e.g., electrical, magnetic, or someother drive) to transmit or to scatter light to create an image forprojection, a Schlieren optics projector (or other projector whichprojects scattered light), and a light transmissive mask or separator toreduce unwanted light scattering by the liquid crystal display device atoptically dead spaces or areas of the drive. Reflected light from theoptically dead spaces may be focused at the mask of the Schlieren opticsand blocked thereby so that such light will not be projected. Exemplaryprojectors or projection systems are mentioned above and are disclosedin several of the above-identified patents and patent applications.

The various patents and patent applications mentioned herein are herebyincorporated in their entireties by reference thereto.

The invention, then, comprises the features described herein thedescription and the annexed drawings set forth in detail certainillustrative embodiments of the invention. These embodiments areindicative, however, of but a few of the various ways in which theprinciples of the invention may be employed.

Although the invention is shown and described with respect to certainembodiments, it is evident that equivalents and modifications will occurto others skilled in the art upon the reading and understanding of thespecification. The present invention includes all such equivalents andmodifications

BRIEF DESCRIPTION OF THE DRAWINGS

In the annexed drawings:

FIG. 1 is a schematic illustration of a Schlieren optics projectorsharing the specular light path;

FIG. 2 is a schematic illustration of a Schlieren optics projectorsharing both scattered light and specular light paths;

FIG. 3 is a schematic side elevation view of an active matrix liquidcrystal display;

FIG. 4 is an enlarged view of a part of the active matrix display ofFIG. 3;

FIG. 5 is a plan view of the liquid crystal device used in the displayof FIGS. 3 and 4;

FIGS. 6 and 7 are section views of the liquid crystal device lookinggenerally in the direction of arrows 6—6 and 7—7 of FIG. 5,respectively;

FIGS. 8 and 9 are schematic section view illustrations of a pictureelement of the display of FIGS. 3 and 4 respectively in the lighttransmitting and light scattering states or modes;

FIG. 10 is a schematic illustration of apparatus to make a liquidcrystal device with an integral separator or mask;

FIG. 11 is a plan view of a photographic mask for use in the apparatusof FIG. 10;

FIG. 12 is a schematic illustration of an embodiment of liquid crystalprojector in accordance with the invention;

FIG. 13 is a schematic illustration of an alternate embodiment of liquidcrystal projector in accordance with the invention;

FIGS. 14 and 15 are graphical representations of the light scatterdistribution for several film thicknesses of NCAP device, the data inthe graphs of both figures being the same, but the scale of FIG. 15being expanded relative to the scale of FIG. 14;

FIG. 16 is a graph illustrating the transfer of light from the scatterto the specular for a 20 micron thick NCAP device;

FIG. 17 is a graph showing the impact of birefringence on refractionangle for a spherical device, such as a liquid crystal materialcontained in a generally spherical containment medium, and in a sense isa plot of the refraction cone angle vs. the light energy containedwithin that cone for different liquid crystal birefringence;

FIG. 18 is a graph illustrating the impact of liquid crystalbirefringence on the width of NCAP scatter distributions for twodifferent NCAP films, one with relatively high and the other withrelatively low birefringence; and

FIG. 19 is a graph illustrating scatter energy distribution for twodifferent NCAP films, respectively, having relatively high birefringenceand relatively low birefringence.

DESCRIPTION

In referring to the drawings, which are schematic, like referencenumerals designate like parts in the several figures, and the sameprimed and unprimed reference numerals usually designate parts which aresimilar in form or function.

Turning to FIGS. 1 and 2, an exemplary Schlieren optics projector 10 inaccordance with an embodiment of the invention includes a light source11, a lens system 12, including, for example, a condenser lens 13 and acollection and projection lens 14, a reflective scattering device orsystem 15, and Schlieren optics 16. A separator 17 (sometimes referredto as a mask) which does not scatter light is associated with thescattering device 15. In FIG. 1 the scattering device 15 is shown indotted outline so the path of light 20 in the projector 10 absentscattering easily can be seen. In FIG. 2 the paths of unscattered light(sometimes referred to as specular light) and of scattered light areshown.

Light 20 from the light source 11 is directed by the condenser lens 13via a mirror 21 to the collection/projection lens 14 which collimatesthe incident light 21 i and directs the collimated light to thescattering device 15. The scattering device 15 is selectively operableto scatter light or not to scatter light. The scattered light will bepassed by Schlieren optics 16 for projection to a projection screen 22,and the light which is not scattered by the scattering device 15specular light is blocked from projection. The separator does notscatter light, and the specular light therefrom also is blocked fromprojection.

The scattering device 15 may have some light reflecting characteristicsand/or may include a mirror 23 or some other type of reflective meanswhich reflects light that has passed through the scattering device, backthrough the scattering device for delivery to the Schlieren optics 16.Exemplary light paths for respective portions of the reflected lightare, as follows:

-   -   i. Phantom lines 24 t represent specular light, e.g., light that        is not scattered by the device 15; and    -   ii. Dash lines 24 s represent scattered light, e.g., light that        is scattered by the device 15.

The scattered light 24 s is collected by the collection lens 14 and isprojected by that lens (and by one or more additional optical elements,such as lenses, mirrors, etc.) toward the screen 22 to form a brightspot 24 b corresponding to a picture element or area of the scatteringdevice 15 which is in the scattering mode. A collection of such brightspots 24 b forms the relatively bright areas of the projected image atthe screen 22. Specular light 24 t from picture elements or areas of thescattering device 15, which are in the light transmissive(non-scattering) mode, is collected by the lens 14 and is directed tothe mirror 21 of the Schlieren optics 16. These light transmissive modeareas of the scattering device 15 correspond to the relatively darkareas of the projected image at the screen 22.

Referring to FIGS. 3-7, the scattering device 15 is shown schematically.The scattering device 15 is a liquid crystal display system 30 whichincludes a liquid crystal device 31 and an electrical drive 32. Theelectrical drive 32 is a TFT active matrix electrical drive system whichincludes a plurality of controlled electrodes 33 and one or moretransparent counter electrodes (sometimes referred to as groundelectrodes, etc.) 34. The electrodes 33 are selectively connected to asource of electrical energy by one or more respective transistors 35which are controlled by and which receive power from power and controlcircuitry 36. Between respective electrodes 33 is space 37. The spaces37 provide electrical insulation between electrodes 33 and also providea place where conductors or conductive paths may be located, as isconventional in active matrix drives. The electrodes 33, transistors 35,electrically conductive paths (such as electrical conductors) andpossibly other electrical and/or electronic components are located onand/or in a semi-conductor substrate 38. The substrate 38 and componentsthereof may be referred to collectively as an active matrix substrate 39or active matrix drive. Various types of active matrix drives are knownand may be used in the invention. Several examples are disclosed in U.S.Pat. Nos. 5,532,854 and 5,519,524. Power and control circuitry 36provides controlled operation of the respective transistors 35 and theselective delivery of electrical power or energy to and/or appropriateground connections, for example, for the respective electrodes 33, 34,as may be conventional in an active matrix drive for a liquid crystaldisplay.

The electrodes 33 may be optically reflective or may include a coatingof an optically reflective material to reflect light received via theliquid crystal device 31 back into the liquid crystal device. Similarly,light reflecting properties may be included and/or inherent in the space37, for example, by a light reflecting characteristic of the surface ofthe semi-conductor substrate 38 in the area of the space 37, lightreflecting characteristics of the conductors and/or other devices in thearea of the space 37, and/or a separate light reflective coating there.Various means are known in the art to obtain such reflection, as it isknown to use active matrix drives for reflective liquid crystal displaysystems. Thus, various conventional or other means may be employed toprovide the light reflecting characteristics for the system 30.Moreover, it is possible that the space and/or the conductors and/orother means in the space 37 are not optically reflective and that lightreceived via the liquid crystal device 31 in the area of the space 37 isnot reflective.

The liquid crystal device 31 includes a plurality of picture elements50, sometimes referred to as pixels or picture areas, etc. Each pictureelement 50 is formed of one or more volumes 51 of liquid crystalmaterial 52 in a medium 53. The medium 53 is optically transparent andhas an index of refraction. The liquid crystal material 52 is nematicliquid crystal or is operationally nematic (meaning liquid crystal thathas operational characteristics that are the same or similar to those ofnematic liquid crystal, for example). Also, the liquid crystal materialpreferably is birefringent, has an ordinary index of refraction which isthe same as or is substantially the same as (matches or is substantiallymatched to) the index of refraction of the medium 53 and anextraordinary index of refraction which is different from the index ofrefraction of the medium 53. Further, the liquid crystal material 51 haspositive dielectric anisotropy. Examples of volumes of liquid crystalmaterial 52 in a medium 53, operation and cooperation thereof and themaking and using thereof are described, for example, in a number of theabove-mentioned patents and patent application including, for example,U.S. Pat. Nos. 4,435,047 (Fergason) and 4,728,547 (Vaz), and U.S. Pat.Application No. 60/040,764.

Summarizing operation of the liquid crystal display system 30,considering one of the picture elements 50, if no electric field isapplied between the electrode 33 and the counter electrode 34 associatedwith such picture element, the liquid crystal material 52 is in a randomorientation so as to cause refraction or scattering of light as thelight transmits through the picture element. The scattered light isreflected back through the picture element, for example, by thereflective electrode 33 or by some other reflective means, and isfurther scattered. The scattered light exits the picture element at thetransparent electrode 34 and is collected by the collection lens 14 andprojected toward the screen 22. However, if a suitable electric field isapplied by a respective electrode 33 and counter electrode 34, incidentlight 21 i is transmitted through the picture element without scatteringor without substantial scattering to the respective reflective electrode33 (or other reflective means), and is reflected back through thepicture element 50 as unscattered (specular) light 24 t (FIGS. 1 and 2)for delivery via the collection lens 14 to the mirror 21 which serves asa stop for the Schlieren optics 16. By selectively applying or notapplying electric field to the liquid crystal in respective pictureelements 50, the non-scattering (transmissive) and scattering modes ofthe respective picture elements can be determined. There are noelectrodes 33 in the area of the optically dead space 37, as such spaceis used for conductors, electrical insulation, and/or other purposes; ifliquid crystal volumes were in the area between the optically dead space37 and the counter electrode 34 such volumes would scatter light whichis undesirable because such light does not contribute to the projectedimage and reduces contrast of the projected image. The separator 17 isbetween respective picture elements 50 in the area of optically deadspace 37 to reduce or to avoid light scattering from the area ofoptically dead space.

The separator 17 includes a plurality of segments which separate pictureelements from respective relatively adjacent picture elements, as isseen most clearly in FIGS. 4-7. The segments of the separator 17 may bein the form of a matrix seen in the top plan view provided in FIG. 5such that the respective segments 55 thereof are aligned with respectivespaces 37. Preferably the separator 17 does not usually change itsaffect on light transmitted therethrough as the electrodes 33 and 34cooperate to apply electric field to respective picture elements 50.Moreover, preferably the separator 17 does not scatter light. Therefore,incident light 21 i (FIGS. 1 and 2) that is received by the separatorand may be reflected by some means in the optically dead space 37returns essentially in the same path as the specular light 24 t, and theSchlieren optics blocks that specular light from the projection screenas is shown, for example, in FIG. 2.

The relationship of the Schlieren optics 16 and the optics used todirect incident light to the scattering device 15 is illustrated hereinsuch that the incident light 21 i is collimated and is incident on thescattering device so as to be substantially normal or perpendicular tothe surface thereof and to the reflector mechanism, such as mirror 23,reflective characteristics of the electrodes 33, etc. This arrangementfacilitates the Schlieren optics such that incident light 21i which isnot scattered and is reflected as specular light 24 t conveniently isstopped by the mirror 21 from projection to the screen 22 and rather isdirected out of the projection's system. Other arrangements also couldbe used whereby the incident light is provided at a different anglerelative to the scattering device 15 and reflective mechanism 23, forexample, and/or the incident light may be provided as other thancollimated light, as will be appreciated.

In FIG. 8 is schematically shown a single picture element 50 a having anelectric field E across the volumes of liquid crystal thereof (two ofwhich are illustrated to avoid cluttering the drawing). The electricfield is provided by the circuitry 36 (FIG. 3), conductive paths (notshown), transistor 35, electrode 33, and counter electrode 34 associatedwith the picture element 50 a. The electric field E is suitable to causethe liquid crystal material 52 in the volumes 51 thereof to align totransmit light without scattering or without substantial scattering.Accordingly, incident light 21 i is transmitted through the pictureelement 50 a and is reflected as specular light 24 t which travelssubstantially in the same path as the incident light. As was describedabove, the specular light 24 t is collected by the lens 14 and isdirected to the mirror 21 for reflection out of the projection systemand does not reach the screen 22. As for the incident light 21 i′ whichis directed through a segment 55 a of the separator 17 adjacent orbounding the picture element FIG. 50 a, such incident light istransmitted through the segment without scattering or at least withoutsubstantial scattering. Such light may be absorbed by means in theoptically dead space 37, and in such case, such light does not reach thescreen 22. Such incident light 21 i′ may be reflected by mirror 23 orsome other means, for example, at or near the surface of thesemiconductor substrate 38 as specular light 24 t′ along the same pathas the incident light 21 i′. Such specular light 24 t′ is collected bythe lens 14 and is directed to the mirror 21 for reflection out of theprojection system so as not to reach the screen 22. The operation of thesegment 55 a would be substantially the same for the other segments 55of the separator 17.

In FIG. 9 is illustrated schematically operation of the pixel 50 a whenthe volumes of liquid crystal therein are in a scattering mode. Only twoof those volumes 51 are schematically illustrated in FIG. 9 to avoidcluttering the drawing. In this illustration, electric field is notbeing applied and the volumes of liquid crystal are in a scatteringmode. Incident light 21 i enters the pixel 50 a and to some extent isscattered by the volumes of liquid crystal. The path of scattered lightis exemplified by lines 21 i′ and 24 s. Light is reflected by the mirror23, the reflective electrode 33, or by some other means. Scattered light24 s exits the picture element 50 a in a direction that is not parallelto the originally incident light 21 i. Such scattered light 24 s iscollected by the lens 14 and is projected past the mirror 21 to thescreen 22 to form a bright area 24 b (FIG. 2). The incident light 21 i′that is directed to the segment 55 a and the reflected specular light 24t′ follow the paths that were described above with respect to FIG. 8 andsuch specular light 24 t′ is collected by the lens 14 and is directed tothe mirror 21 for removal from the projection system so that such lightdoes not reach the screen 22.

Exemplary liquid crystal materials, polymer or other medium in whichvolumes of liquid crystal may be contained, combinations thereof, andmethods for making that may be used in the invention are disclosed inthe several patents and patent application mentioned herein. Severalexamples of liquid crystal, polymer medium and methods are describedbelow. Other liquid crystal materials, media and methods may be used tocarry out the principles of the invention.

EXAMPLE 1

A polymer PN393, which is an ultraviolet curable polymer, is mixed withliquid crystal material ZLI2244, which is a nematic liquid crystal thatis birefringent, has positive dielectric anisotropy, and an ordinaryindex of refraction which is substantially matched to that of thepolymer when the polymer has been cured. The polymer and liquid crystalare weighted out in proportions of 20% polymer to 80% liquid crystal.The mixture is shaken to cause thorough blending. The mixture may bestored in a dark storage area.

Two pieces of clean ITO (Indium Tin Oxide) coated glass plates or sheetsare placed in parallel confronting sandwich-like relation, spaced apartby spacers that are five micrometers (microns). The glass plates arerectangular (an exemplary size is about one inch by one inch, but sizeis not a limitation), and two pairs of opposite edges are sealed byapplying Norland 70UV curable adhesive and exposing it to ultravioletlight for fifteen minutes to obtain sufficient curing and, thus, forminga cell. The interior of the cell is open at the unsealed opposite edges.In a dark room the liquid crystal and polymer mixture is placed at oneopen end of the cell and the cell is filled by capillary action. Afterfilling, the cell is exposed to ultraviolet light for about two to threehours to achieve suitable curing. The two edges from which the cell isfilled then are sealed by applying ultraviolet curable adhesive andexposing it to ultraviolet light for about fifteen minutes to achievesufficient curing.

The liquid crystal cell is operable to scatter light in the absence ofan electric field applied between the ITO electrodes of the glassplates; and it is operable to reduce scattering in the presence of asuitable electrical field.

EXAMPLE 2

A liquid crystal cell is constructed and tested as described in Example1 except that the spacers are three microns.

EXAMPLE 3

A liquid crystal cell is constructed and tested as described in Example1 except that the spacers are eight microns.

The refractive index of the PN393 polymer is 1.473. The extraordinaryindex of refraction of ZLI2244 is 1.556, the birefringence is 0.08, andthe ordinary index of refraction is 1.476, which is substantiallymatched to that of the polymer. As was mentioned above other materialsmay be used. Also, as for the PN393 polymer, that material initially isa monomer before curing using UV light. Curing in this case is across-linking. There are other types of curing, several examples ofwhich include cross-linking, reacting, drying, heating, etc. An exampleof a process for making the liquid crystal device using UV light forcuring is described in U.S. Pat. No. 4,728,547 (Vaz).

Turning to FIGS. 10 and 11, an exemplary apparatus 60 and method formaking the liquid crystal device in place on an active matrixsemiconductor substrate drive 32 is illustrated schematically at 60. Theapparatus 60 includes a holder 61, a mask 62, and an illumination system63. The holder 61 holds the active matrix substrate 38 and the blend 64of polymer and liquid crystal, such as that described in the aboveexamples, in position to be exposed to the ultraviolet light applied bythe illumination system 63 for curing. The holder 61 may include, forexample, a support 65 and several walls 66, which hold the active matrixsubstrate 38 and blend 64 in position and preferably provide a seal toprevent the blend from leaking down along the sides of the active matrixsubstrate 39. The height of the walls 66 is sufficient to contain adesired depth of the blend 64. Since the blend may be applied as aliquid or fluidic phase, it may fill the optically dead spaces 37.Therefore, it is possible for the blend to follow the contour of thesurface of the active matrix display 38, for example, contacting therespective electrodes 33 and also filling the optically dead space 37.In some prior art active matrix liquid crystal display systems,techniques were used to planarize the surface of the active matrixsubstrate, for example, to fill in the optically dead space to a levelto be coplanar with the electrodes, but such technique may not be neededin the present invention due to the filling of the optically dead spaceby the blend material 64.

It has been discovered that different portions of the blend 64 can becured differently to achieve different physical characteristics. Forexample, the portions of the blend 64 which are to be the separator 17segments 55 can be cured before the portions which will become thepicture elements 50. Initially the portions which form the separator 17can be cured at a relatively slow rate, for example, using low intensityultraviolet light. That slow rate allows liquid crystal material that isincluded in the polymer to be forced out of the polymer as the polymercures, and such liquid crystal material migrates to the portion of theblend which is not then being cured, namely portions that will be thepicture elements 50. The portions of the blend 50 will be the pictureelements 50 can be cured subsequently.

The blend 64 is cured using the illumination system 63. The illuminationsystem 63 includes a source of ultraviolet light 70 and one or morelenses 71 to magnify, demagnify and/or collimate the light. Initiallylight is directed via the mask 60 to the blend 64. The mask 62 includeslight transmissive portions 72 and light blocking portions 73. The lighttransmissive portions 72 are aligned with those areas of the blend 64which are to form the separator 17. The light blocking portions 73 arealigned with those portions of the blend 64 which are to form thepicture elements 50. A control 74 is provided for the ultraviolet lightsource 70. The control 74 may control the intensity of the ultravioletlight source and/or the time or duration that the light source suppliesultraviolet light. To control intensity, the control may include adiaphragm or aperture mechanism and to control duration, the control mayinclude a timer to time the period in which the light source 70 isenergized. A dimmer type control also may be used, such as a controlthat periodically pulses the light source 70. Various other controls maybe used. The mask may be prepared by photographic techniques, such asthose used to make masks for selective exposure of emulsions used in theprocess for fabricating semiconductor devices. The mask may be anotherdevice which selectively transmits and blocks transmission of theultraviolet to respective portions of the blend 64. The function of thecontrol 74 may be supplemented or substituted by the opacity of thetransmissive portion of 72 of the mask 62. The size of the mask 62 andof the respective transmissive and non-transmissive portions 72, 73thereof may be determined by the size of the display device 31, thepicture elements 50 and the separator 17 segments 55. Size also may bedetermined by the nature of the illumination system 63, such as whetherthe lens system 71 magnifies, demagnifies, collimates, focuses, etc.light incident on and/or transmitted through the mask 62. In theillustrated embodiment the mask 62 is larger than the area of the blend64 in the holder 61, and the lens system 71 includes a diffuser 75 whichdiffuses light from the source 70 and delivers the light to the mask 62,a demagnifying lens 76 and a collimating lens 77 by which a collimatedlight pattern conforming to the mask 62 is directed to the blend 64.

Initially, the system 60 is used to expose portions of the blend 64which will form the separator 54. Accordingly, ultraviolet light ofappropriate intensity is directed via the lens system 71 and through thetransmissive portions of the mask 62 to the blend 64. As the polymer inthe exposed portions of the blend is cured at a relatively slow rate,the curing process tends to force out of the polymer liquid crystalmaterial, which migrates to the portion of the blend 64 which are notthen being cured. Some of the liquid crystal material may remain in theportions of the blend which form the separator 17, but that amount isrelatively small and usually is insufficient to form volumes of theliquid crystal that would change optical characteristics when the device31 is used.

After the separator has been formed by sufficient curing, the mask 62may be removed, and the entire blend 64 may be exposed to ultravioletlight. This subsequent exposure is preferably at a sufficiently highintensity or rate that volumes of the liquid crystal tend to form in thepolymer. An example of such formation is described in theabove-mentioned U.S. Pat. No. 4,728,547 (Vaz).

It will be appreciated that other techniques also may be used to makethe liquid crystal device 31 so as to have multiple portions includingplural picture elements 50 and separator 17. Furthermore, it will beappreciated that a separator 17 with segments 55 that transmit lightwithout scattering or without substantial scattering (or even lightabsorbing separators) may be used to separate respective pictureelements and/or to tend to preclude light from the optically dead spacebeing projected as light output in other types of displays, especiallyprojection displays.

The projector 10 may include additional or different optical elementsthan those illustrated in FIG. 1 and described above. For example, othertypes of projection, collimating, condenser, etc. lenses or lens systemsmay be used; reflectors which have properties of focusing light may beused with or substituted for lenses. Various stops and/or other meansmay be used in the Schlieren optics portion of the projector todiscriminate between light that is scattered by the liquid crystaldisplay and light which is unscattered. Also, it will be appreciatedthat such discrimination includes determining the angle at which suchscattering must occur, e.g., a minimum angle, for such scattered lightto bypass the Schlieren optics stop to allow such light to be projected.Also, although the separator 17 of the invention is illustrated anddescribed with respect to a reflective type of liquid crystal displaysystem and associated Schlieren optics, it will be appreciated that theseparator principles may be used with transmissive type liquid crystaldisplays and other optics and projection systems. Furthermore, althoughthe separator is illustrated and described with respect to a liquidcrystal type of display system, it will be appreciated that principlesof the invention may be used with other types of displays.

The liquid crystal display 30 is selectively operable to scatter lightor to reduce scattering (preferably to eliminate scattering or at leastsubstantially to eliminate scattering and, thus, to transmit lightwithout substantial scattering). The volumes 51 of liquid crystal 52 inmedium 53 may be separate or discrete; they may be interconnected; theymay be respective areas or portions in a relatively large volumetricspace, may be that volumetric space, and so forth. In the scatteringmode, the display 30 scatters light for projection by the projector 10(FIG. 1); and in the non-scattering mode, the display transmits lightwithout scattering or with a relatively small amount of scattering sothat preferably light at the areas of the display which are in thenon-scattering mode will be blocked by the Schlieren optics 16 and willnot be projected to the projection screen 22.

In an embodiment the scattering device 15 is a liquid crystal displaysystem. However, it will be appreciated that other devices may be usedto provide the functions of selectively scattering or transmitting lightand of reflecting and/or otherwise directing the scattered andunscattered light to the Schlieren optics 16 or other discriminator sothat the desired light is projected and light that is not desired to beprojected will not be projected. Other electrical or electronic drivesmay be used in addition or alternatively to those described herein.

Referring to FIG. 12, a projector in accordance with an embodiment ofthe present invention is generally indicated at 101. The projector 101includes a light source 102, a condenser 103, a liquid crystal device104, a further condenser 105, a ring aperture 106, and projection optics107. Light 110 from the light source 102 is modulated by the liquidcrystal device 104, and the modulated light 111 is discriminated by theaperture 106 to separate specular light, which is blocked, fromscattered light which is projected by the projection optics 107 as alight output 112. The light output 112 may be directed to a screen orother device where it may be viewed or otherwise utilized.

The light source 102 may be an incandescent lamp, an arc lamp, or someother source of light. The light source 102 and condenser 103 cooperateto provide collimated light 110 c, which is incident on the liquidcrystal device 104. The light source 102 and condenser 103 are oneexample of a light source or supply to provide the collimated light 110c; it will be appreciated that other means may be used to provide suchcollimated light, such as, for example, various types of light emittingdevices, lamps, lenses, reflectors, baffle systems, remote sources oflight lasers, and so forth. In the exemplary embodiment illustrated inFIG. 12, the condenser 103 is a lens and the light source is positionedrelative to the lens such that the light output therefore is collimatedor is substantially collimated.

The liquid crystal device 104 transmits the light which is incidentthereon or scatters the light that is incident thereon. The transmittedlight (specular light) is represented at 111 t and the scattered lightis represented at 111 s. Depending on the operative condition of theliquid crystal device 104 or respective portions thereof incident light110 c will be transmitted 111 t or scattered 111 s. The light 111 fromthe liquid crystal device 104 is directed via the further condenser 105to the aperture 106.

In the illustrated embodiment of projector 101 the aperture 106 is aring aperture in which a generally annular opening 113 is formed in amask 114. At the center of the annular opening 113 is a stop 115. Thefurther condenser 105 and the aperture 106 cooperate such that thefurther condenser 105 focuses the transmitted light 111 t at or near thestop 115, whereby the stop is able to block further transmitting of suchlight beyond the stop and aperture 106. The further condenser 105 andaperture 106 also are cooperative such that the scattered light 111 s isdirected by the further condenser through the opening 113 in theaperture 106 as light 117. The light 117 is projected by the projectionlens 107 as the light output 112 of the projector 101. The light output112 may be directed to a screen on which an image for covering is formedor may be otherwise utilized.

The liquid crystal device 104 is described hereinafter as an NCAP liquidcrystal device, several examples of which are disclosed in the aboveU.S. patents, and as is known, such devices sometimes are referred to ascomposites, PDLC, LCPC, and possibly by other names or acronyms.However, other liquid crystal devices of the type which has operativemodes to scatter light and to transit light may be used. For brevity inthis description, though, reference to NCAP device collectively refersto all aforementioned liquid crystal devices. Another type of liquidcrystal device useful in the projectors described herein providesvariable optical polarization features as are described in U.S. Pat.Nos. 5,113,270, 5,479,277 and 5,523,863; these and all other patents areapplications referred to herein are incorporated entirely by references.

As is described in further detail below, relative control of the angleover which light is scattered by the liquid crystal device may beachieved by using relatively low birefringence liquid crystal materialin the NCAP device, controlling or selecting the size of the volumes ofliquid crystal and/or controlling or selecting the thickness of theliquid crystal device. In an exemplary NCAP device volumes of liquidcrystal material and another medium cooperate to cause light scatteringdue to index of refraction differences. In such an exemplary device theliquid crystal material is birefringent; the extraordinary index ofrefraction is different from the index of refraction of the medium, andthe alignment, organization, etc. of the liquid crystal is influenced bythe medium, whereby incident light is scattered. However, in suchexemplary device the ordinary index of refraction is matched orsubstantially matched to the index of refraction so that when alignmentof the liquid crystal is appropriate, e.g., in response to a prescribedinput, scattering decreases. Scattering may occur due to the mismatchbetween the index of refraction of the medium and the extraordinaryindex of refraction of the liquid crystal material; and a decrease inscattering may occur due to the closer matching of the ordinary index ofrefraction to the index of refraction of the medium compared to thelarger difference between the extraordinary index and the index of themedium.

In an embodiment of the invention the birefringence of the liquidcrystal is about 0.12 or less. More preferably it is about 0.08 or less.Even more preferably it is between about 0.04 and about 0.08.

In an embodiment of the invention the liquid crystal volumes are about 5microns or less in size or diameter. The size of the volumes. may beabout 4 microns or less. The size also may be about 3 microns or less.These sizes are, of course, approximate. The volumes may be spherical oranother shape. The volumes may or may not be interconnected; or some mayand some may not be interconnected. The volumes may be discrete or not.The volumes may be volumetric areas or space in a matrix of the medium.The size of the volumes may affect the density of the scattering sitesfor a given thickness of liquid crystal device; the smaller thescattering sites or scattering centers, the more scattering that isobtained.

In an embodiment the liquid crystal material may be nematic, smectic,cholesteric, operationally nematic, operationally smectic, oroperationally cholesteric, smectic A or other material operative in thecontext of the invention. In an embodiment the liquid crystal materialis nematic liquid crystal which has positive dielectric anisotropy.Other liquid crystal materials also may be used.

The medium may be any of many different materials, as is known. Examplesinclude polyvinyl alcohol, polymer, resin, epoxy, urethane and others.

In the projector 101 illustrated in FIG. 12 light 10 from a small lightsource 102 is collimated by the condenser lens 103. When the NCAP liquidcrystal device 104, which may be considered, for example, a lightmodulator or a display type of device, is in its clear state, the lightremains collimated as it passes to the further condenser lens 105. Thisfurther condenser lens 105 then refocuses the light back to a small spot120. The stop 115 of the ring aperture 6 is located at this focal pointand blocks any light transmission of such specular light 111 t. Anylight 111 s scattered by the NCAP device 104, is directed by the furcondenser lens 105 through the ring aperture 106 to the projection lens107. The further condenser lens 105 and projection lens 107 combine tofocus an image of the NCAP device 104 on a projection screen (notshown). The focal distance can be adjusted by changing the spacingbetween these two lenses.

It will be appreciated that although lenses are illustrated anddescribed herein for various optical functions, other equivalent devicesmay be equivalently used; examples are one or more reflectors,combinations of lenses, of reflectors or of both lenses and reflectors,and so forth.

Another optical phenomenon that can degrade the performance of the darkstate of the projector 101 is diffraction. When the NCAP device 104 isdivided into pixels for display purposes, an isolated clear pixel candiffract a very small fraction of the light passing through it. Thediffracted light will no longer be parallel to the original beam and thefurther condenser lens 105 will not focus it onto the stop 115. Insteadit would pass through the ring aperture 106, and would be collected bythe projection lens 107 for projection, thus possibly reducing contrastor otherwise degrading the projected image. This problem can beameliorated by placing an appropriate phase plate 121 at the ringaperture 106, as is schematically shown as an embodiment possibility forthe projector 101 of FIG. 12. This phase plate 21 acts as a spatialfilter and can eliminate or reduce the effect of such diffraction.

An alternate embodiment of projector 101′ is illustrated in FIG. 13. InFIG. 13 primed reference numerals designate parts that are similar orthe same in form and function as corresponding parts designated byunprimed reference numerals in FIG. 12. The projector 101′ is used in areflective mode, as illustrated in FIG. 13.

As is seen in FIG. 13, a plain mirror 130 is placed on the back side 104b of the NCAP device 104′, which is now illuminated from the front side104 f. Only a single condenser lens 103′ is required in the projector101′. The single condenser lens 103′ performs two separate functions. Itcollimates the light from the source 103′ and also refocuses thecollimated light reflected from the display device 131, for example,including the NCAP device 104′ and the mirror 130, onto the stop 115′ ofring aperture 106′. A beam splitter 132 allows the source and reflectedbeams to overlap. An advantage of the reflection mode is that it permitsthe thickness of the NCAP device 104′, e.g., the one or more layer(s) ofliquid crystal material or volumes of liquid crystal thereof, to be of areduced thickness, e.g., compared to the thickness of the NCAP device104 of the projector 101 of the FIG. 12 embodiment, and such reductionin thickness can result in a reduction in the required drive voltage forthe NCAP device. This is because the light now makes two passes throughthe liquid crystal device 104′. The main disadvantage is that thedistance between the NCAP cell and the projection lens 107 is increased,raising the light collection f#.

One significant limitation of this system, is that any light that isscattered into too large of an angle will not hit the entrance pupil ofthe projection lens, and is lost. Therefore it is desirable to have anNCAP device with a narrow scatter distribution. This will allow aprojection lens of reasonable f# to capture more of the scattered lightenergy.

The pattern of light scatter in NCAP devices is controlled by severalfactors and differs in several ways from common passive scatteringmaterials. The primary factors are voltage, thickness, particle size,and liquid crystal birefringence. Light photons passing through an NCAPcell (sometimes the NCAP device may be referred to herein as a cell oreven as a layer) are segregated into three distinct populations. Onesegment of the photon population sees no scattering at all. It passesthrough the cell in a completely specular fashion (transmitted light orspecular light). The photons in the second group participate inprecisely one scattering event each. The photons in the third groupengage in multiple scattering events. The relative sizes of these groupsare determined principally by the thickness of the NCAP layer and thevoltage across it. The angular distribution of the photons in group twois controlled by the liquid crystal particle size and the birefringence.

For a very thin NCAP cell with no voltage applied, the photon populationdistribution is dominated by the unscattered fraction. Most of theremaining photons are involved in single scatter events. Very fewphotons are multiple scattered. As the thickness of the NCAP layer isincreased photons are shifted from the unscattered group to the singlescatter group. For a substantial portion of the thickness range, thereis little transfer to the multiple scatter group. As a result the shapeof the angular distribution of photons changes little. The relativeamplitudes of the scattered and unscattered populations change, but thewidth of the distribution for each does not. As the cell thicknessincreases beyond this range, a significant amount of multiple scatterbegins to occur. Since the multiple scatter distribution is much widerthan the single scatter distribution, the composite distribution widensas the NCAP thickness grows. The single and multiple scatterdistributions overlap and are not easily distinguishable. In the limit,all photons are multiple scattered, leading to a Lambertiandistribution. An example of this trend is illustrated in FIGS. 14 and 15using a series of NCAP cells of varying thickness, made using the sameliquid crystal (E49). These graphs are plots of luminous intensity vs.scatter angle (as measured from the normal). A Lambertian diffuser wouldproduce a cosine curve on the type of plot. FIGS. 14 and 15 present thesame data but on different scales. The feature to be noted in FIG. 14 isthe size if the spike centered at 0°. This represents the amount ofunscattered light. The increased scale of FIG. 15 makes it easier to seethe shape of the scattered portion of the distribution. When the curvesfor the 7 and 20 micron thick NCAP film samples are compared, asubstantial difference in the amplitudes of the unscattered specularpeaks can be seen. Yet, the shape of the angular scatter is almost thesame, with only a change of amplitude, corresponding to the transferfrom the specular population. This indicates that most of the scatteredphotons have undergone only one scatter event. The curve for the 26micron thick sample begins to show a change of character. The specularpeak is almost gone and the width of the scatter has widened, indicatinga significant increase in multiple scattering. The 35 micron sampleshows a complete absence of specular photons and the width of thescatter distribution indicates that multiple scatter is now dominant.

The voltage response mimics the thickness response. The voltage is thevoltage of electric field applied across the liquid crystal example asthe prescribed input. There is a small voltage threshold, below which nochange in the scatter distribution occurs. As voltage is increase beyondthe threshold, photons are transferred from the multiple scatter groupto the single scatter group and from the single scatter group to thespecular group. The transfer of light from the scatter to the specularis graphed for a 20 micron cell in FIG. 16. As can be seen, there is aknee at about 3 times the threshold voltage. Above that level thetransfer process goes asymptotically to a limit. As with thickness,changes in the applied voltage do not change the distribution width ofany of the three photon populations. Only the relative amplitudes arechanged. The dependence of the width of the scatter distribution onparticle size and liquid crystal birefringence can be understood bythinking of each scatter event as refraction by a spherical lens. Thefocal length of a spherical lens is proportional to its radius andinversely proportional to its index of refraction. The angle throughwhich the lens refracts any given ray of light increases with decreasingfocal length and with increasing distance between the incident point andthe center line of the lens. The liquid crystal material isbirefringent. Its ordinary index of refraction is matched to the indexof refraction of the binder, medium, or containment medium. Theextraordinary index of refraction is somewhat higher. The “index ofrefraction” may be referred to as “index” below. When the NCAP film isin the low voltage, high scatter, state, the director of the liquidcrystal droplet lies in or near the plain of the film. As a result,light rays entering the film at normal incidence will see theextraordinary index as the index of the particle. For rays off normal,the index will he slightly lower. While the liquid crystal particles inNCAP films are oblate spheroids, rather than true spheres, the generaltrend can be illustrated by looking at refraction by a sphere with indexof refraction equal the liquid crystal extraordinary index imbedded in amedia with an index equal to the ordinary index.

FIG. 17 shows the impact birefringent on refraction angle. In this plotR is distance of the incident point on the sphere from the center line.The light energy refracted inside a given exit angle is proportional tothe projected area of a circle of radius R on the input of the sphere.That area is in turn proportional to R². Effectively this is a plot ofthe refraction cone angle vs. the light energy contained within thatcone for different liquid crystal birefringence. As can be seen, higherthe birefringence, produces a wider the distribution of light energy.

FIG. 18 illustrates the impact of liquid crystal birefringence on thewidth of NCAP scatter distributions. This shows the scatter for two NCAPfilms, one with high and the other with low birefringence. Thebirefringence of E49 and 4119 are 0.25 and 0.06 respectively. Each filmis chosen with thickness such that the distribution is dominated by thesingle scatter mode, with a small amount of specular leak through.Clearly the lower birefringence material has a much narrower scatterdistribution. To determine the correlation of scatter width on theefficiency of the projector, one may convert the intensity plot to anenergy density plot. This is done by multiplying the intensity at agiven angle by the solid angle of a differential annular ring at thatangle. This transformation is performed in FIG. 19. The light collectionefficiency for a projector lens of a given f# depends on the amount ofenergy that falls within its entrance pupil. Most of the energy from thelow birefringence NCAP would be captured by an f 1.4 lens. For the highbirefringence NCAP most of the energy would not. Notice that there isvery little energy contributed by the very center of the distribution.This means the stop 115 in the center of the ring aperture will blockvery little of the scattered light.

An advantage of the low birefringence NCAP Schlieren projector of thetype described, is that it can provide high contrast images withextremely thin NCAP layers. In turn this allows low voltage drivecircuits to be used. Also, a high intensity light source can be used,because there is negligible absorption in NCAP material. The narrowscatter angle of the low birefringence NCAP leads to a high collectionefficiency with a reasonable size projection lens. The bright sourcecombined with the efficient collection yield a bright projected image.

An example of light source 102 may be, for example, a metal halide lightsource. To facilitate collimation of light directed to the liquidcrystal device the light source 103 may be located at the focal point ofthe condenser 103 lens; the accuracy of such positioning, though, mayvary with the extent of collimation desired. For example, if haze is notof concern and it is not necessary to have the incident light normal tothe liquid crystal device, then other arrangements of the light sourceand condenser may be employed. Similarly, the function of the furthercondenser 105 is to direct light that was not scattered by the liquidcrystal device 104 to the stop 115. The precise positioning of thefurther condenser 105 and the stop 115 may be varied, provided suchfunction is obtained; however, in an embodiment of the invention, thefurther condenser receives the specular or transmitted light ascollimated or substantially collimated, and the stop 115 is positionedat the focal point of the further condenser so that such focusing ofsuch light thereat is obtained.

The projection optics 107 may be a single projection lens or acombination of lenses, reflectors or other elements that project thelight output 112 for the desired purpose, such as to provide an image ona screen or some other purpose.

The distance between the NCAP device 4 and the condenser 103 ofprojector 101 is not critical. The distance between the NCAP device 104and the condenser 103′ of projector 101′ preferably is such that theimage of the NCAP device can be in effect focused at the screen ontowhich the output light 112 is directed.

The illustration in FIG. 15 indicates that there is bleed through in thecenter if a thin NCAP device is used until the thickness gets to beabout 35 microns thick. However, for such a thick NCAP device, there isincreased voltage required, which may increase cost of the projector;there also may be more than a nominal increased cost for the liquidcrystal material itself.

Desirably the liquid crystal material used gives the optimum output andcontrast with respect to an output, e.g., output optics, of a particularf number.

Moreover, although the aperture 106 may be a ring aperture having agenerally annular opening 113 in a mask or plate 114 with a central stop115, it may be possible to eliminate the plate 114 itself. In such case,the central stop 115 blocks specular light; and the collected scatteredlight for projection by the projection optics 107 may be determined bythe size and/or f number of the projection optics itself. Therefore, theaperture may be defined by the stop and a light transmitting areaadjacent the stop, and the radial extent or remote limit or distance ofthe light transmitting area of the aperture is limited by the f numberof the projection optics. Also, the aperture may be absent an externaldefining element, and the entrance pupil of the projection optics limitsthe amount of light that is collected from the aperture.

The relatively thin NCAP device useful in the invention permits the useof a relatively low drive voltage. Due to the cooperation of the liquidcrystal device and the ring aperture, the output light 112 provides abright image; there is relatively little bleed through that woulddegrade contrast, e.g., compared to the leakage of prior center apertureprojectors mentioned above. Also, since the liquid crystal device can berather thin, the amount of energy dissipated therein is rather small,and, accordingly, rather bright light sources can be used withoutcausing a burn out of the liquid crystal device due to excess heat orenergy dissipation in the liquid crystal device; this in combinationwith the ring aperture arrangement allows a substantial amount of lightto be put through the projector to provide a bright output.

The central stop 115 may be supported in the annular opening 113 byvarious means. One example is a spider type of support. Another exampleis to use a glass or other transparent material in the opening area andof the plate 114 and to place an optically non-transmissive material atthe center area of such material to serve as the stop 115. Also, ifdesired, a light pipe, reflector, or some other device may be placed inthe area of the stop 115 to conduct light directed thereto away from thelight path leading to the projection optics.

Further, although in the projectors hereof a separate projection optics107 is disclosed, it will be appreciated that the lens of the furthercondenser 105 may be coordinated with the other components of theprojector to provide the projection function without the need forseparate projection optics or with the modification of the projectionoptics.

The invention also embodies drive circuitry for driving the liquidcrystal device 4. Such circuitry may comprise one or more conductors,integrated circuit devices, thin film transistors or other devices,other solid state devices, other electrical devices or components, videocircuitry, television circuitry, computer, electrodes, and so forth.Such circuitry may be used to drive the liquid crystal device and togenerate the signals to drive the device, e.g., to develop an image forprojection.

Also, the liquid crystal device may be a plurality of such devicesoperated simultaneously or sequentially or both to provide monochrome,color or multicolor output light and images.

1. A liquid crystal display system, comprising a substrate having pluralelectrodes in spaced apart relation, plural volumes of liquid crystal ina medium, said volumes of liquid crystal arranged in overlying relationto respective electrodes, said volumes of liquid crystal beingselectively operable to scatter light or to transmit light withoutsubstantial scattering, a mask between respective groups of volumes ofliquid crystal, said mask being in overlying relation to said substrateand between respective electrodes such that the mask covers saidsubstrate at least substantially up to a lateral boundary of eachelectrode.
 2. The system of claim 1, said mask being substantiallytransparent.
 3. The system of claim 1, said mask being substantiallynon-scattering, said volumes being operative to scatter light in theabsence of a prescribed input, and said volumes being operative toreduce scattering in response to a prescribed input.
 4. The system ofclaim 1, wherein said liquid crystal comprises liquid crystal materialhaving a birefringence of about 0.12 or less.
 5. The system of claim 1,wherein said liquid crystal display includes a medium having pluralvolumes containing the liquid crystal material, an angle of the lightscattering being a function of the size of the volumes, and wherein thesize of the volumes is about 5 microns or less.
 6. The system of claim1, wherein said liquid crystal comprises liquid crystal material havinga birefringence between about 0.04 to about 0.08.
 7. The system of claim1, wherein the volumes of liquid crystal comprise liquid crystalmaterial of relatively low birefringence in a medium that has surfacesto cause scattering of light in the absence of a prescribed input andreduces scattering in response to the prescribed input, wherein thesurfaces interact with the liquid crystal material to cause scatteringof light, and wherein the surfaces interact with the liquid crystalmaterial to cause scattering of light due to a difference between theextraordinary index of refraction of the liquid crystal material and theindex of refraction of the material of the surfaces.
 8. The system ofclaim 1, wherein the ordinary index of refraction of the liquid crystalis substantially matched to the index of refraction of the medium, andwherein the liquid crystal has positive dielectric anisotropy.
 9. Thesystem of claim 1, wherein the liquid crystal is operationally nematic,operationally smectic or cholesteric.
 10. The system of claim 1, whereinthe mask is a separator comprised of the medium.
 11. The system of claim1, wherein the mask is laterally in direct contact with the electrodes.12. The system of claim 1, wherein electrical components for driving theelectrodes are at least partly vertically aligned with a space betweenadjacent picture elements, and the mask overlying the portions of theelectrical components that are vertically aligned in the space tooptically mask the portions of the electrical components that arevertically aligned with the space.
 13. A liquid crystal display for aSchlieren projection display system, comprising: plural liquid crystalpicture elements selectively operable to affect light by scattering orabsorbing light or by reducing such scattering or absorption of light; aseparator integral with and between respective picture elements, saidseparator being substantially non-selectively operable to affect light,and defines an inherent mask of lateral spacers between respectivepicture elements thereby forming a grid of spacers and picture elements;and plural electrodes in spaced relation for selectively applyingelectrical input to respective picture elements; wherein: said liquidcrystal picture elements comprising liquid crystal and a medium that arecooperative for selective operation to scatter light for projection orto reduce such scattering or absorption, and said inherent masktransmits light between respective picture elements without substantialscattering.
 14. The liquid crystal display for a Schlieren projectiondisplay system of claim 13, wherein the integral separator is comprisedof the medium of the liquid picture elements.
 15. The liquid crystaldisplay for a Schlieren projection display system of claim 13, whereinthe integral separator is laterally in direct contact with theelectrodes.
 16. The liquid crystal display for a Schlieren projectiondisplay system of claim 13, wherein the spacers of the separator cover asubstrate of the liquid crystal display at least substantially up to alateral boundary of each electrode.
 17. The liquid crystal display for aSchlieren projection display system of claim 13, wherein the inherentmask optically masks the space between respective electrodes bytransmitting light without substantial scattering.
 18. The liquidcrystal display for a Schlieren projection display system of claim 13,wherein electrical components for driving the electrodes are at leastpartly vertically aligned with the space between adjacent pictureelements, and said separator overlying the portions of the electricalcomponents that are vertically aligned in the space to optically maskthe portions of the electrical components that are vertically alignedwith the space.
 19. A liquid crystal display, comprising: plural liquidcrystal picture elements selectively operable to affect light byscattering or absorbing light or by reducing such scattering orabsorption of lights; a separator integral with and between respectivepicture elements, said separator being substantially non-selectivelyoperable to affect light and said separator comprising lateral spacersbetween respective picture elements thereby forming a grid of spacersand picture elements; and plural electrodes in spaced relation forselectively applying electrical input to respective picture elements;wherein said spacers spacer means being located in relation to the spacebetween respective electrodes; and electrical components for driving theelectrodes are at least partly vertically aligned with the space betweenadjacent picture elements, and said separator overlying the portions ofthe electrical components that are vertically aligned in the space tooptically mask the portions of the electrical components that arevertically aligned with the space.
 20. A liquid crystal display,comprising: plural liquid crystal picture elements selectively operableto affect light by scattering or absorbing light or by reducing suchscattering or absorption of light; a separator integral with and betweenrespective picture elements, said separator being substantiallynon-selectively operable to affect light, and said separator comprisinglateral spacers between respective picture elements thereby forming agrid of spacers and picture elements; and plural electrodes in spacedrelation for selectively applying electrical input to respective pictureelements; wherein said spacers spacer means being located in relationthe space between respective electrodes; and the picture elementscomprise liquid crystal and a medium, and the integral separator iscomprised of the medium of the liquid picture elements.
 21. The displayof claim 20, said separator defining an inherent mask between respectivepicture elements.
 22. The liquid crystal display of claim 20, whereinthe integral separator is laterally in direct contact with theelectrodes.
 23. A liquid crystal display, comprising: plural liquidcrystal picture elements selectively operable to affect light byscattering or absorbing light or by reducing such scattering orabsorption of light; a separator integral with and between respectivepicture elements, said separator being substantially non-selectivelyoperable to affect light, and said separator comprising lateral spacersbetween respective picture elements thereby forming a grid of spacersand picture elements; and plural electrodes in spaced relation forselectively applying electrical input to respective picture elements;wherein said spacers spacer means being located in relation to the spacebetween respective electrodes; and the spacers of the separator cover asubstrate of the liquid crystal display at least substantially up to alateral boundary of each electrode.
 24. A liquid crystal display,comprising: plural liquid crystal picture elements selectively operableto affect light by scattering or absorbing light or by reducing suchscattering or absorption of lights; a separator integral with andbetween respective picture elements, said separator being substantiallynon-selectively operable to affect light, and said separator comprisinglateral spacers between respective picture elements thereby forming agrid of spacers and picture elements; and plural electrodes in spacedrelation for selectively applying electrical input to respective pictureelements; wherein said spacers spacer means being located in relation tothe space between respective electrodes; and wherein the separatoroptically masks the space between respective electrodes by transmittinglight without substantial scattering.
 25. A liquid crystal display,comprising: a plurality of picture elements comprised of liquid crystalin a medium, each picture element separated from adjacent pictureelements by portions of the medium that are substantially free of liquidcrystal; and a plurality of electrodes disposed with respect to thepicture elements to selectively apply electrical input to the pictureelements; wherein electrical components for driving the electrodes areat least partly vertically aligned with a space between adjacent pictureelements, and the portions of the medium that are substantially free ofliquid crystal overlying the portions of the electrical components thatare vertically aligned in the space to optically mask the portions ofthe electrical components that are vertically aligned with the space.26. A liquid crystal display, comprising: a plurality of pictureelements comprised of liquid crystal in a medium, each picture elementseparated from adjacent picture elements by portions of the medium thatare substantially free of liquid crystal; and a plurality of electrodesdisposed with respect to the picture elements to selectively applyelectrical input to the picture elements; wherein the picture elementsare operative to scatter light or transmit light by reducing scatteringbased on the electrical input, and the portions of the medium that aresubstantially free of liquid crystal are operative only to transmitlight without substantial scattering.